Vasorelaxant effects of diarylheptanoids, acerogenin A and (−)‐centrolobol from the bark of Acer nikoense

Abstract

ABSTRACTAimThe bark of Acer nikoense (Aceraceae) is used in Japanese folk medicine as a remedy for hepatic disorders and eye diseases. The aim of this study was to investigate the vasorelaxant effects of A. nikoense extracts and further clarify the active constituents and mechanisms of action.MethodsDried A. nikoense bark was extracted with methanol. The extract was further extracted with diethyl ether, ethyl acetate, and 1‐butanol, successively. The major constituents of the extracts were isolated using chromatography. Vasorelaxant effects of the extracts and isolated constituents were assessed using isolated rat aorta. The aorta was placed in a well‐oxygenated bath of modified Krebs–Henseleit solution and the mechanical tension measured isometrically.ResultsThe extracts had a vasorelaxant effect on aorta precontracted with 3 × 10−7 mol/L norepinephrine (NE). Isolated major constituents of A. nikoense bark, diarylheptanoids, such as acerogenin A (compound 1), B (compound 2), (−)‐centrolobol (compound 3), aceroside I (compound 5), B1 (compound 6), VII (compound 7) III (compound 8), and phenolic compound, (+)‐rhododendrol (compound 4) were examined. Compounds 1 and 3 had vasorelaxant effects on rat aorta with or without endothelium in the NE‐induced preparation. Furthermore, compounds 1 and 3 inhibited contraction induced by a high concentration (60 mmol/L) of K+ and also had a moderate inhibitory effect on NE‐induced vasoconstriction in the presence of nicardipine.ConclusionThe inhibition of NE‐induced vasoconstriction by compounds 1 and 3 may be attributed to factors such as endothelial independency by blocking of Ca2+ influx via voltage‐dependent Ca2+ channels and receptor‐operated Ca2+ channels.